Backlash clutch and joint mechanism for a robot comprising the clutch

ABSTRACT

A backlash clutch comprising first rotation member ( 3 ) and a second rotation member ( 4 ), each of which are provided rotatably on an identical axis, and are engaged together in a rotating direction of the members by contacting each radial extension surface ( 3   a   , 4   a ). A gap d exists between said radial extension surface of the first and the second rotation members ( 3   a   , 4   a ) at the rotating direction of the members.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a backlash clutch that realizesa high torque transmission characteristic and free joint mechanism. Thisinvention also relates to a free joint mechanism for a robot comprisingthe clutch.

[0003] 2. Description of Related art

[0004] Generally, in a clutch mechanism, connection and disconnectionfor transmitting driving force are achieved by means of a frictionmechanism. Such a friction mechanism comprises rotating members that arejoined together by frictional function acts between the members tocontrol the on-off action of the clutch. In such a clutch mechanism,using frictional action it has been difficult to transmit the force whenthe force is large because slippage arises at the clutch mechanismtransmits a driving force.

[0005] This phenomenon generates a significant problem when a clutchmechanism applies to a knee joint of a humanoid robot. Typically, in ahumanoid robot, such a joint mechanism provided in the body is driven bycontrolling actuators to generate objective paths. Especially, there isused an actuator which generates high power to the knee joint.

[0006] When the humanoid robot rests with the posture shown at FIG. 9,assuming that the weight of the upper part from the articulatio coxae is60 kgf and the offset length from the articulatio coxae to the kneejoint is 10 cm, under the acceleration of gravity is 9.81 m/s², there isrequired that the actuator drives the knee joint which must output hightorque such as 58.86 Nm. Therefore, the knee joint mechanism must have acapability to transmit such a high torque.

[0007] In general, the knee joint mechanism is composed from a motorgenerating high power and reduction gears with a high gear ratio. On theother hand, in a human's walking motion, the knee joint of a leg acts asa free joint when the leg is not grounding. It is contemplated that suchan action of the knee joint has the following effects;

[0008] There is no need to use extra force.

[0009] When a human moves forward a leg, the knee of the leg movesfreely in accordance with an inertial force.

[0010] When the leg touches down, an impulsive force acts on the legthat is eased up because the leg will head for ground at an adequateangle, naturally.

[0011] However, the present knee joint mechanism has difficulties torealize a free joint following a reactive force, where the walkingmotion is performed to control maintaining the knee with a controlleddesired angle when the leg is not grounding.

[0012] To ensure that the knee joint has such a free moving condition,it is contemplated to incorporate a clutch mechanism into the reductiongears. However, a general clutch mechanism is a friction using type suchas the above-mentioned clutch, it generates slip at high torque, so thatit is difficult to transmit high torque. Therefore, the clutch mechanismcan only be attached to the input shaft side of the reduction gears.Consequently, the knee joint of a humanoid robot needs a clutchmechanism that can provide to output on the shaft side of the reductiongears as a mechanism that can achieve both to transmit high torque andto maintain a free moving condition.

[0013] It is therefore an objective of the present invention to providea clutch mechanism possible to transmit high torque and maintain a freemoving condition, and a joint mechanism of a robot comprising such aclutch mechanism. Especially, the object of this clutch mechanism is torealize a walking motion and has the following advantages when it isused as a knee joint;

[0014] (1) Transmit a large driving force

[0015] (2) Achieving a free joint,

[0016] (a) Needs not to use extra force.

[0017] (b) Realize free motion

[0018] (c) Absorbing an impulsive force at landing

SUMMARY OF THE INVENTION

[0019] A backlash clutch of this invention which achieves advantageouslythe above-mentioned object comprising a first rotation member and asecond rotation member, each of which is provided rotatably on anidentical axis, and is engaged together in a rotating direction of themembers by contacting each radial extension surface, a gap between saidradially extension surfaces of the first and the second rotation membersin the rotating direction of the members.

[0020] According to this backlash clutch, the relative rotation of thefirst and second rotation member which rotate until the gap between saidradial extension surfaces of these rotation members in the rotatingdirection of these members is a backlash, this backlash is able toachieve the following effects;

[0021] (a) Achieve a free joint.

[0022] (b) Transmit a high torque when the clutch is in a coupledcondition.

[0023] A joint mechanism for a robot comprising the backlash clutchaccording to claim 1, two composing members form an arm or a leg of arobot and are connected together rotatably, one of the composing memberssupports one of said first and second rotation members rotatably at therotation axis of the composing member, another one of the composingmembers fixes the other one of said first and second rotation members,and, the joint mechanism further comprising a drive means driving one ofsaid first and second rotation members rotatably relative to thecomposing member which supports said rotation members rotatably.

[0024] According to this a joint mechanism for a robot comprising such abacklash clutch, the following effects can be obtained;

[0025] (c) Realize a reaction force-following the mechanism follows thereaction force by a free joint.

[0026] (d) Absorb impulsive force by means of the reaction forcefollowing the motion of the reaction force-following mechanism.

[0027] (e) Avoid consumption of unprofitable energy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a schematic front view showing a knee joint mechanism ofa humanoid robot as one embodiment of the backlash clutch and the robotcomprising the clutch according to the present invention.

[0029]FIG. 2 is a schematic diagram of the knee joint mechanism shown inFIG. 1, which transmits torque at the peripheral gap between the radialextension surfaces of the first and the second rotation members and iszero.

[0030]FIG. 3 is a schematic diagram of the knee joint mechanism shown inFIGS. 1 and 2, showing that the joint is in a free joint condition.

[0031]FIG. 4 is a relation diagram of the knee joint mechanism shown inFIGS. 1-3, showing a preferable example of control to make the jointmechanism in a free joint condition.

[0032]FIG. 5a is a schematic diagram showing a leg of a humanoid robotthat intends to ground, and FIG. 5b is a schematic view of part A ofFIG. 5a enlarged.

[0033]FIG. 6a is a schematic diagram showing an action of the knee jointmechanism of the present invention when a leg of a humanoid robotintends to grounding, and FIG. 6b is a schematic view of part B of FIG.6a enlarged.

[0034]FIG. 7 is a schematic diagram showing a motion of a leg ofhumanoid robot after the leg is raised from the floor as a rear foot.

[0035]FIG. 8 is a schematic diagram showing a further motion of a leg inFIG. 7.

[0036]FIG. 9 is a schematic diagram showing a pose of the humanoid robotwhen the robot bends its knee.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0037] The present invention will be further explained below withreference to a preferred embodiment shown in the accompanying drawings.FIG. 1 is a schematic front view showing a knee joint mechanism ofhumanoid robot as one embodiment of the backlash clutch and the robotcomprising the clutch according to the present invention. In FIG. 1,numeral 1 represents an upper part of a leg as one member and consistsof one leg of a humanoid robot, numeral 2 represents a lower part of aleg as another part of the member consists of said leg, and this lowerpart of leg is rotatably connected together with upper part of legaround the axis C. Numeral 3 represents a first rotation member andconsists of a backlash clutch of the embodiment of this invention;numeral 4 represents a second rotation member and consists of a backlashclutch of the embodiment of this invention. Numeral 5 represents apulley provided to output a shaft of high output power motor withreduction gears, and numeral 6 represents a belt.

[0038] In this knee joint mechanism, first rotation member 3 and secondrotation member 4 are located on identical axis C to be able to rotaterelatively, first rotation member 3 is rotatably supported by upper partof leg 1 around the axis C, second rotation member 4 is fixedlyintegrated with lower part of leg 2. Furthermore, first rotation member3 and second rotation member 4 have radial extension surfaces 3 a, 4 a,respectively, and both surfaces contact each other, and a gap (backlash)is formed between said rotation members at the direction of saidrotation members.

[0039] Additionally, a belt transmission mechanism using a high poweroutput motor with reduction gears having said pulley 5, pulley 5 andsaid belt 6 consists of a drive means, and said first and secondrotation members, said motor and said drive means consists of a saidknee joint mechanism of the embodiment. In this embodiment, said drivemeans is configured by transmitting output power of said motor to saidfirst rotation member 3 via pulley 5 and belt 6, however, the drivemeans of the knee joint mechanism for robot of this invention is notlimited to the aforementioned drive means.

[0040] The backlash clutch and the knee joint mechanism for a robot ofthis embodiment, transmit rotation and realize a free condition areachieved by the following procedure.

[0041] (1) Transmit Driving Force

[0042] In this joint mechanism, as shown in FIG. 2, torque istransmitted to the direction represented by the arrow in the drawing bymeans of setting the peripheral gap d between the radial extensionsurface 3 a of the first rotation member 3 and the radial extensionsurface 4 a of the second rotation member 4 as zero (for convenience,this gap was depicted to exist slightly between said surfaces). In thiscase, the first rotation member 3 and second rotation member 4 lead tomake surface contact by contacting radial extension surfaces 3 a, and 4a to each other so that the surfaces are perpendicular to the directionof the rotating force so that these members ensure to transmit largetorque. In this joint mechanism, since the direction of transmitting thedriving force is in one way, response with a time lag arises if thismechanism uses a servomechanism to control the rotation angle. However,in this mechanism such as a knee joint of a humanoid robot, saidrotating force always acts to a constant direction so that this jointmechanism is performed effectively. This joint mechanism is suited tomaintain the pose of a condition of bending the knee to transmit a hightorque as shown in FIG. 9.

[0043] (2) Realize Free Moving Condition

[0044] In such a joint mechanism, as shown in FIGS. 3a-3 c, for example,joint at free condition is realized by controlling the rotation angle ofthe first rotation member 3 to maintain the gap d to the constant valued₀ adapted to rotation of the second rotation member 4 caused by a swingof the lower part of leg 2. In general, an actuator with reduction gearshaving high gear ratio to output a high torque cannot generate arevolving speed as much as maintain the gap d to a constant valueagainst free motion of the lower part of leg 2. However, this jointmechanism of this invention is able to realize a free condition of legbecause this joint has a margin of gap corresponding to the value ofbacklash. That is, if the rotation angle of the upper part of leg is θ,rotation angle of the lower part of leg is φ; angle of gap for thedirection of rotation is ψ, if θ is controlled to satisfy the equation

θ·φ=ψψ₀

[0045] for predetermined angle (backlash) ψ₀, a free joint is realized.

[0046] For example, an exemplary control shown in FIG. 4, amplitude of θis small by comparison with rotation angle of φ, and the value ofamplitude of θ follows that of φ with phase retardation. However, thevalue ψ which is difference value between θ and φ is within ψ₀ (=±0.2radian), so that free moving joint condition has been realized.

[0047] According to above-mentioned backlash clutch of the embodiment,realizing a free joint by incorporating this clutch to a knee joint of ahuman robot, impact shock act on leg at grounding as following reasons.That is, suppose, as shown in FIG. 5a, the leg that is not groundinggoes in for grounding. In this time, as shown in FIG. 5b, the bottom ofthe leg will make a line contact with the floor. If the knee joint iscontrolled by a high output actuator and to perform a desired rotationangle, a large impact force generated and act on the grounding line madeby contact of the leg and the ground, so that the leg is raised byrepulsive force from the floor when the floor or the bottom of the legis made from hard material. On the other hand, if a free joint isapplied to the knew joint, the knee joint will perform the motionfollowing a repulsive force from the floor (repulsive force followingmotion) shown in FIG. 6a, and the bottom of the leg will ground byachieving surface contact with the floor. Thus, the effect to absorbimpulsive force from the floor is obtained.

[0048] On the other hand, a when a leg (right leg of the humanoid robotin drawing) which is not grounding makes a heel to the floor, the legcreates the following paths.

[0049] (1) At first, a femoral area of the leg is raised so as to theleg will not contact the ground, and the knee is bent as shown in FIG.7,

[0050] (2) Second, the knee is held out in order to pull up the leg.

[0051] Generally, in an adequately controlled knee joint, theabove-mentioned bending and pulling up motion is controlled by thecontrolling rotation angle of the knee joint, and this joint representsdesired paths given by the designer. However, since this motion of aknee joint is essentially natural motion that is generated by gravityand inertial force, it is generated automatically by making this kneejoint to have free motion. Consequently, it is understood that theeffective walking motion of a humanoid robot without extra force isachieved by realizing a free joint.

[0052] According to the backlash clutch of this embodiment, by usingthis clutch, the following advantageous effect is obtained:

[0053] (a) Achieve a free joint.

[0054] (b) Transmit a high torque when the clutch is in a coupledcondition.

[0055] Moreover, according to the knee joint mechanism for a robot ofthis embodiment, the following advantageous effects are obtained:

[0056] (c) Realize a reaction force-following the mechanism follows thereaction force by a free joint.

[0057] (d) Absorb impulsive force by means of the reaction forcefollowing motion of the reaction force-following mechanism.

[0058] (e) Avoid consumption of unprofitable energy.

[0059] While the present invention has been described above withreference to a specific embodiment shown in the accompanying drawings,this invention is not limited by the above-mentioned embodiment. In themechanism of this invention it can be constructed that the firstrotation member can be integrally fixed to the upper part of leg and thesecond rotation member to be rotatably supported by the lower part ofleg and to be driven by the driving means. And in this embodiment, thesecond rotation member is located inside of the first rotation member,and each of the radial extension surfaces of these members areconfigured at the convexity part provided in their inner surface of thefirst rotation member and the outer surface of the second rotationmember respectively. Alternatively, the first and second rotationmembers may be located parallel to the direction of axis for rotation,and their radial extension surfaces may be formed at the convexity partprovided on the surface of the members that face each other.

[0060] Furthermore, this backlash clutch of the present invention canapply to the mechanism except for the joint of a robot, and the jointmechanism for a robot can be used to realize a free swing motion of anarm of a robot except for a leg of a humanoid robot.

1. A backlash clutch comprising; A first rotation member and a secondrotation member, each of which arc provided rotatably on an identicalaxis, and are engaged together in a rotating direction of the members bycontacting each radial extension surface, wherein, A gap between saidradially extension surfaces of the first and the second rotation membersat the rotating direction of the members.
 2. A joint mechanism for arobot comprising the backlash clutch according to claim 1, wherein, Twocomposing members form an arm or a leg of a robot and are connectedtogether rotatably, One of the composing members is supporting one ofsaid first and second rotation members rotatably at the rotation axis ofthe composing member, Another one of the composing members fixes theother one of said first and second rotation members, and, The jointmechanism further comprises a drive means driving one of said first andsecond rotation members rotatably relative to the composing member whichsupports said rotation member rotatably.